I7o PRACTICAL ORGANIC CHEMISTRY is gradually added to the warm solution.*1 The cuprous cyanide dissolves in excess of the potassium cyanide and cyanogen g'as is liberated. 2CuSO4 + 4KCN = 2CuCN + 2K2S04 + (CN)2- The solution is left, whilst the /-toluidine is diazotised. The base is dissolved in the dilute hydrochloric acid, cooled, in ice, and well stirred. The mixture is kept cold whilst the sodium nitrite solution is gradually added, until it gives an immediate colouration with potassium iodide-starch paper. The clia-zo- solution is then added in portions of about 10 c.c. at a time to the warm cuprous cyanide solution, with frequent shaking. A rapid effervescence occurs, nitrogen and some hydrocyanic acid being evolved. When, in the course of a/bout fifteen minutes, the diazo-solution has been added, it is left on the water-bath until effervescence ceases (J hour). The liquid turns a dark colour, and a black tarry deposit is formed. The product is distilled in steam. This should be carried out in the fume cupboard, as not only is hydrocyanic acid liberated, but a small quantity of isocyanide, which is formed inthe reaction, and produces an intolerable smell. The distillation is continued until no more yellow oil passes over. The tolyl cyanide solidifies in the receiver on cooling as a yellow crystal- line mass, which is filtered, dried on a porous plate, and may be purified by distillation ; but for the preparation of toluic acid this is unnecessary. Yield about 15 grams. CH3.C0H4NHo.HCl + NaN02+ HC1 = CH3.CflH4N2CHh Properties.— Colourless crystals ; m. p. 29° ; b. p. 218°. Reaction. — p-Toluic Acid. — Boil up 10 grams tolylcyanide with a mixture of 30 c.c. cone, sulphuric acid and 20 c.c. water, in a. round flask with upright condenser until colourless crystals of toluic acid appear in the condenser tube (about half an hour). On cooling, the acid crystallises out, and is separated by filtration, washed with water, and recrystallised from hot water ; m. p. I 79°. CH3.CGH4.CN + 2HoO -1- H9S04 = CH3.C6H4.CO.OM + NH4.H.SOi. if | The yield is nearly theoretical.